PROJECT SUMMARY/ABSTRACT Radiation therapy plays an important role in the management of many cancers. The delivery of safe and effective radiation requires multiple components, though the identification of the radiation target (tumor), and areas to avoid (normal tissues) represents a critical step in this process. Accuracy with target delineation ? commonly referred to as contouring ? requires sound understanding of anatomy, radiology, and most importantly the individual patient. Research clearly shows that poor contouring leads to increased toxicity, and decreased survival, which emphasizes the consequence of contouring quality. This proposed project aims to create a user-friendly web-based imaging resource for contouring in radiation oncology. Our proposed tool will entail a searchable library of individual patient cases, each of which will include 3D imaging and contours defining tumor and normal tissues. Additionally, we will create focused content for each individual case describing the rationale behind contour delineation. We will pilot, widely deploy, and evaluate the efficacy of this contouring tool among the greater radiation oncology community. This project will develop an educational resource with the overall goal of improving the quality of contouring in radiation oncology, which ultimately stands to improve quality and safety of radiation therapy.